1. Field of the Invention
This invention lies in the field of mineral mining. More particularly, it is concerned with a system of mineral mining in which a relatively short working shaft is provided which is started regularly from the bottom of a vertical or slope shaft extending from the surface. A wall in a mineral strata is cut away either by long wall techniques or by short wall techniques and the working face is in a sense rotated radially until a complete cylindrical portion of the seam is removed.
2. Description of the Prior Art
In the prior art many systems of mining minerals such as coal have been advanced. Elaborate mining machinery has been developed such as the continuous miner which can cut a short wall equal to the width of its cutting cylinder or sidewall cutters which can advance along the long wall. However, the subsurface is generally worked by a room and pillar method or a number of parallel horizontal shafts are first drilled by conventional methods and wide sections are cut back by a long wall, short wall, auger, and/or other conventional methods.
There are a number of areas in which improvements can be made in these types of operations, such as, roof falls, complete recovery, fresh air, shortest route, fire and maintenance. One of them involves the great length of roadway and transport that is required to bring in supplies and to carry out minerals from the working face to the mouth of the mine, which is greatly reduced by this invention.
Furthermore, the national average for recovery of these minerals is between 50 and 70% of the inplace material, which with this method the recovery can be virtually 100%. The reason for the poor recovery by conventional methods is because the material which is left cannot be recovered without excessive cost and/or endangering life by roof falls.
In the prior art systems there is great difficulty and expense in maintaining a safe roof, so that it does not fall and kill people, or cave in from the side. A consequence of the prior art systems is that the roof must be supported for the life of the mine since succeeding production is delivered through the areas of prior production.
In this invention, as soon as a long wall is advanced a selected distance the roof supporting means are moved, to an adjacent position, permitting the roof to cave, since there is no transport of material or personnel through that area.
And finally, there is the problem of maintenance, of the roof, of the mine proper, of the transport means and transport routes, electrical power, water, track, gas buildup, etc. Since all these routes are shortened in this invention, the maintenance is greatly simplified.
The conventional methods of mining have great fire hazards due to dust, spontaneous combustion, dead air spaces, worn or frayed electrical cables or other electrical equipment, etc. In this system the ventilation system is short and direct, permitting more rapid and complete changes of air.